The present invention relates to a workpiece positioner, an apparatus for moving and manipulating one or more workpieces to a predetermined position and orientation with respect to an industrial robot in automated manufacturing and/or processing operations.
In the prior art, a variety of workpiece positioners have been developed to work with industrial robots. For example, one common workpiece positioner is known as a “Ferris-wheel positioner.” Such a positioner has a generally H-shaped frame structure with at least two sets of workpiece supports for supporting a pair of workpieces between the “legs” of the H-shaped frame structure. Thus, each workpiece can be independently rotated about a horizontal axis, while the H-shaped frame structure itself can also be rotated about a horizontal axis (i.e., an “exchange axis”).
Another common positioner is a “three-axis table,” which also has a generally H-shaped frame structure that can again itself be rotated about a horizontal axis. Furthermore, the H-shaped frame structure is mounted on a table, allowing for rotation of the entire H-shaped frame structure about a vertical axis.
As recognized and discussed in U.S. Pat. No. 5,873,569 issued to Boyd et al., such prior art positioners encounter problems when workpiece sizes approach the maximum work envelope of the associated industrial robot. For example, with respect to a Ferris-wheel positioner, since floor clearance determines the maximum size of the workpiece that can be rotated about a horizontal axis, as the workpiece size increases, more floor clearance is required. To account for the required floor clearance, the frame structure must be raised, and the robot operation height may become inconveniently high.
For another example, with respect to a three-axis table, adequate clearance between the positioner and robot is required to allow the positioner to rotate about its vertical axis. As the workpiece size increases, additional clearance and distance is required to allow for the rotation about the vertical axis. To account for the required clearance, the proximity of the robot to the workpiece is compromised, thus requiring the robot to be moved during the rotation of the positioner or foregoing optimum reach.
To address such problems associated with work space and clearance, U.S. Pat. No. 5,873,569 issued to Boyd et al. teaches a construction in which the rotary workpiece holder includes a first end and a second end, with upper and lower cross members (e.g., tie bars) fixed to and extending between the first and second ends of the workpiece holder. These cross members impart the rotation of the first end (i.e., drive end) to the second end (i.e., idler end) of the workpiece holder. More importantly, these cross members are located substantially outside of a planar area defined by the workpiece supports mounted on the first and second ends of the workpiece holder, thus allowing the workpiece-to-workpiece rotational clearance to be near zero. However, because of the positioning of these cross members a substantial distance away from the axis of rotation of the workpiece holder, and considering the significant mass of the cross members that is required to transmit torque from the drive end to the idler end of the workpiece holder, the result is a significant moment of inertia. Accordingly, the drive forces required to start or stop the rotational motion of workpiece holder are substantially increased.
Another solution is proposed in U.S. Pat. No. 6,281,474 issued to Michael et al. In the '474 patent, the workpiece positioner is also designed to allow for more efficient use of space by optimizing the size of the work envelope through which a workpiece may be rotated. Specifically, the workpiece positioner includes a rotary framework with opposite rotary framework ends, a first set of workpiece supports, and a second set of workpiece supports. The first set of workpiece supports is positioned on opposite ones of the rotary framework ends so as to define a first workpiece axis, and the second set of workpiece supports is also positioned on opposite ones of the rotary framework ends so as to define a second workpiece axis. The rotary framework further includes a crossing structure secured to the opposite rotary framework ends and extending along the longitudinal framework axis. In order to achieve the objective of optimizing the size of the work envelope through which a workpiece may be rotated, the transverse cross section of the supportive sheet material has a generally “X” shape, converging in the direction of the common workpiece plane so as to optimize the diametrical dimension of the respective rotary envelopes of workpieces supported by the first and second sets of workpiece supports. However, this is a somewhat complex structure that is not easy to manufacture or assemble.